The present invention relates to a method and an apparatus for the combustion of liquid, gaseous or atomized fuels, hereafter referred to as fluidal fuels.
As early as in 1961 F. H. Reynst mentioned that it had been recently recognized that acoustic vibrations have a beneficial effect on combustion. In this connection reference is made to Pulsating Combustion, pp. 13-15, The Collected Works of F. H. Reynst, Pergamon Press, New York 1961. Although the vibrations may be only very weak, the relative motion of the gas with respect to the fuel particle which results is sufficient to remove the envelope of combustion products around this particle, resulting in an increase of the combustion rate. Reynst describes the application of this principle to a pulverized coal burner. A mixture of fuel and air is delivered by a fan to a precombustion chamber located between two conical passages flaring in the direction of flow. Volatile components of the fuel are combusted in the precombustion chamber, and the flame is directed into a flame tube. The pulsations of the flame in the precombustion chamber are propagated into the flame tube, wherein the column of gas is set in resonance so as to move relatively with respect to the fuel particles, which speeds up the combustion as mentioned above.
Swedish patent specification No. 7701764-8 (publ. No. 412 635) describes a method of combusting atomized solid, liquid or gaseous fuels, which is based on the principle mentioned by Reynst. According to this patent specification, the vibrations are not generated by the burner flame. Sound energy is supplied to the combustion flame by external means such as a sound emitter, the frequency of the sound ranging from infrasonic frequencies to ultrasonic frequencies. However, the method of Swedish patent specification 7701764-8 apparently has not yet been utilized in practice to any significant extent, which may indicate that it has not been possible so far to develop the method for industrial application.
Similar methods are described in Swiss patent specification No. 281,373 and German patent specification No. 472,812. According to the Swiss patent specification, vibration is imparted to at least part of the combustion chamber and the flue gases, and according to the German patent specification, a dispersion of particulate fuel and combustion air as well as secondary combustion air is brought to oscillate.
The USSR Author's Certificate No. 228,216 (V. S. Severyanin) describes a pulsating combustion in a bed whereby the hot grid of the Rijke tube is replaced by a layer of solid fuel in which free oscillation will develop. The effect obtained is, however, relatively low, because only self-generated oscillation is utilized.
U.S. Pat. No. 2,945,459 discloses a pulsating combustion method and apparatus wherein pulsating air is supplied to a combustion chamber forming part of a resonance tube receiving the pulsating air. The resonance frequency of the tube is adjusted by means of a plunger closing one end of the tube, the other end being open. The fuel to be combusted is supplied to the air in the resonance tube between the ends thereof.